Плохой файловый дескриптор — простой UDP-клиент

При попытке создать простой UDP-клиент мой код успешно открывает сокет и читает в небольшом буфере файл, который нужно отправить на сервер, указанный по адресу хоста и номеру порта в аргументах командной строки.

Однако и sendto, и recvfrom терпят неудачу с «Bad File Descriptor», и я не могу понять, почему.

void main(int argc, char* argv[]){
int s, n=0, obytes, inbytes;
struct sockaddr_in sin;
char *buffer;
int address = 0;

//Checks socket
if((s = socket(AF_INET, SOCK_DGRAM, 0))<0) {
    printf("Error creating socket\n");
    exit(0);
}
//Resets values in socket structure
memset((char*)&sin, 0, sizeof(sin));
sin.sin_port = htons(atoi(argv[2]));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = inet_addr(argv[1]);
printf("%d\n", sin.sin_addr.s_addr);
/*Opens file to be sent and reads into buffer*/
FILE *readFile;
readFile = fopen(argv[3], "r");
//Checks if file to be read can be opened
if (readFile==NULL) {
    perror ("Error opening file");
}
//Reads in all the characters to a buffer
else{
    while (!feof(readFile)) {
        buffer[n] = fgetc (readFile);
        n++;
    }

buffer[n] = '\0';
printf ("Total number of bytes: %d\n", n);
for(int i = 0; i< n; i++){
    printf("%c", buffer[i]);
}
}
printf("File was opened\n");
//Sends the buffer to the destination designated by the socket structure and checks to see if bytes were sent
if((obytes = sendto(s, buffer, strlen(buffer), 0, (struct sockaddr *)&sin, sizeof(sin))) == -1 ) {
    perror("Sendto() error!");
    exit(1);
}
printf("%d bytes were sent\n",obytes);
//Receives response from the server and checks to see if bytes were actually received
/*  if((inbytes = recvfrom(s, buffer, strlen(buffer)+28, 0, (struct sockaddr *)&sin, sizeof(struct sockaddr*))) == -1 ) {
    perror("Recvfrom() error!");
    exit(1);
}*/
printf("%d bytes were received.\n", inbytes);
//Closes file
fclose (readFile);

}